Printing plate and method of preparation

ABSTRACT

This invention relates to a printing plate of high-wear resistance comprising an aluminum surface which is anodized with sulphuric acid and stabilized in concentrated phosphoric acid and having thereon an ink-receptive image layer. The aluminum surface comprises a cellular structure of alumina-containing pores ranging in size from about 5 to 100 angstroms in average diameter and also comprises about 20 to 5000 mg./meter2 aluminum sulphate and about 1 to 50 mg./meter2 aluminum phosphate. The stabilized anodized aluminum is not only an excellent substrate for a lithographic printing plate but also for letterpress printing plates.

United States Patent [191 Magnotta et a1.

451 Apr. 30, 1974 [22] Filed:

[ PRINTING PLATE AND METHOD OF PREPARATION [75] Inventors: Frank Magnotta, Laurel; Arthur D.

Ketley, Columbia, both of Md.

Mar. 28, 1972 21 Appl. No.: 238,933

[52] US. Cl 96/35, 96/86 R, 96/75, 101/459, 96/115, 204/58 [51] Int. Cl G03c 5/00 [58] Field of Search 96/35.l, 115, 86, 33; 101/459 [56] References Cited UNITED STATES PATENTS 3,511,661 5/1970 Rauner et a1. 96/86 3,619,393 ll/l97l Stably 96/35.l 3,623,879 11/1971 Ketley 96/115 R Primary Examiner.l. Travis Brown Assistant Examiner john L. Goodrow Attorney, Agent, or Firm-Richard P. Plunkett; Kenneth E. Prince ABSTRACT This invention relates to a printing plate of high-wear resistance comprising an aluminum surface which is anodized with sulphuric acid and stabilized in concentrated phosphoric acid and having thereon an inkreceptive image layer. The aluminum surface comprises a cellular structure of a1umina-containing pores ranging in size from about 5 to 100 angstroms in average diameter and also comprises about 20 to 5000 mg./meter aluminum sulphate and about 1 to 50 mg./meter aluminum phosphate. The stabilized anodized aluminum is not only an excellent substrate for a lithographic printing plate but also for letterpress printing plates.

3 Claims, N0 Drawings PRINTING PLATE AND METHOD OF PREPARATION This invention'relates to. an improved anodized aluminum lithographic printing plate. More particularly this invention relates to producing an anodized aluminum lithographic surface which is highly water receptive and shows excellent abrasion resistance and adhesion to photosensitive materials.

In the lithographic printing plate industry, aluminum is generally used as a support for lithographic printing plates because of its low cost, light weight, availability, flexibility and dimensional stability. The water receptivity of the aluminum oxide surface is further improved by anodizing the aluminum in an electrolytic solution.

When an aluminum sheet is anodized in sulphuric acid, the surface is covered by an anodiccoatingof alumina. This alumina is very water receptive, due to the large number of small pores in the surface, and shows excellent abrasion resistance and excellent adhesion to photosensitive materials. Such a surface would be excellent for a lithographic plate were it not that it is unstable, being converted rapidly to boehmite, another form of alumina. Experience has shown that H 50 anodized, unstabilized anodic coatings slowly seal under normal conditions (i.e. 68F, 35%RH) during a period of 6 months, the surface impedance (Z) changing by at least doubling its initial value. These surfaces can also be sealed rapidly by immersion into boiling water for a period of no more than l minutes at which point the surface impedancemay increase to four times its original value. Such sealed surfaces, because of their now low porosity (high impedance) are nolonger able to carry water efficiently or adhere photosensitive materials. On the other hand, aluminum for lithographic plates can be anodized normally using phosphoric acid since the resulting anodic coating is stable. However, phosphoric acid anodizing of aluminum leads to a coating with a small number of relatively large pores which is hence less porous, less abrasion resistant and less desirable.

One object of the instant invention is to produce a lithographic printing plate containing a large number of small pores in the surface. Another object of the instant invention is to produce a litho-plate which is stable still another object is to provide an improved process for the preparation of stabilized and highly hydrophylic anodized lithographic printing plates. A yet further object is to provide an improved anodized aluminum substrate suitable for application of ink-receptive image patterns.

Surprizingly these and other objects have been achieved by subjecting an aluminum plate to anodizing in a sulphuric acid bath and thereafter stabilizing the thus anodized plate in a solution of phosphoric acid. By this means one is thus able to combine the enhanced porosity of the sulphuric acid anodized plate and the stability of the phosphoric acid anodized plate in one element. Lithographic plates prepared in the manner of the instant invention show excellent adhesion on inkreceptive photopolymers and great ability to carry water in the nonimage areas. Their resistance to abrasion and wear on the press is markedly enchanced relative to conventional plates and especially those anodized in phosphoric acid. Furthermore, photopolymer letter press plates prepared using the same substrate also show greatly enhanced adhesion of the polymer to e the substrate. For the most part hereinafter the invention will be explained in terms of forming a lithographic printing plate.

Anodizing of aluminum substrates results in coatings that are essentially aluminum oxide having a cellular structure in which the aluminum surface is completely covered with the aluminum oxide layer. However each cell of aluminum oxide contains a star shaped pore which does not extend completely through the aluminum oxide layer. The average pore size depends upon the electrolytic media used in the anodizing step. To a lesser extent the conditions of anodizing such as electrolytic concentration, voltage, temperature and duration of anodizing can also effect pore size. Since these conditions may be varied, the resulting surface is herein defined in terms of average pore size of the resulting surface.

The average diameter of the pores in the aluminum oxide cells which characterizes the anodized surface of the aluminum of our invention ranges from about 5 to about 100 angstroms which is normal for anodizing in sulphuric acid. The aluminum sulphate which characterizes our improved aluminum lithographic surfaces represents a concentration of from about 20 to about 5000'mg. or more of aluminum sulphate per square me- I ter. The aluminum phosphate which characterizes our obtained by anodizing the aluminum surface in an aqueous solution containing sulphuric acid. The concentration of sulphuric acid can be varied widely. Good results are achieved within the range 5 to percent sulphuric acid. Ordinarily, concentrations of 15 to 20 percent are employed to mitigate repetitive replenishment of the electrolyte.

Following the anodizing step, the sulphuric acid anodized layer is water washed and then immersed into a solution of phosphoric acid for stabilization. The concentration'of the phosphoric acid bath can be varied over a wide range. Excellent stabilization results from an aqueous bath containing 3 to percent phosphoric acid. Generally, concentrations of 15 to 30 percent are used to defer continuous replenishment of the acid in the bath.

Following the stabilization, if desired, a hydrophylic layer suflicient to cover the anodic layer except for certain peaks in the oxide layer extending through the hydrophylic layer may be coated thereon. If desired or necessary, the coating may be of sufficient dimension to overlie the peaks. In the practice of applicants invention, however, it is not generally necessary to use the hydrophylic layer due to the high water receptivity exhibited by the stabilized anodized alumina. Should a hydrophylic layer be employed, various conventional materials can be used including but not limited to ethylene maleic anhydride; polyacrylic acid; carboxymethylcellulose; methylvinyl ether/maleic anhydride copolymer; polylvinybenzal-Z,4-disulfonic acid] sodium salt; and polyacrylamide and the like. These hydrophylic materials are usually applied to whirl-coating in a suitable solvent to yield concentrations in the range 5-100 mgJftF.

After the anodic surface has been stabilized and whether or not a hydrophylic coating is applied thereto,

a light sensitive coating or silver precipitating materials can be placed on the surface. Thus, in addition to the light sensitive materials and silver recipitating materials set out in U.S. Pat. No. 3,511,661 which are operable herein, various other well-known photopolymerizable resins may also be employed. One type of photopolymerizable resin is an organic solvent-soluble ester of an unsaturated acid and a polyalcohol. Examples of such photopolymerizable resins are polyvinyl cinnamate, starch cinnamate, cellulous cinnamate, starch furfurylacrylate, cellulous furfurylacrylate and polyvinyl furfurylacrylate resins. One commercially available example of such a resin is Kodak Photo Resist which is a polyvinyl cinnamate. Another operable light sensitive system is that set out in U.S. Pat. No. 2,760,863 wherein the photopolymerizable layer comprises an addition polymerizable ethylenically unsaturated component and an addition polymerization initiator therefor activatable by actinic light. Still another light sensitive material operable herein is a polyvinyl acetate latex stabilzed with polyvinyl alcohol containing 0.01 to 1.0 part per hundred parts of NH. or K dichromate after drying.

Photocurable compositions are also operable herein as the ink-receptive image area. One such photocurable composition operable is that set out in U.S. Pat. No. 3,627,529 assigned to the same assignee incorporated herein by reference.

The crucial ingredients in the photocurable polymer composition are:

1. 2 to 98 parts by weight of an ethylenically unsaturated polyene containing two or more reactive unsaturated carbon to carbon bonds per molecule;

2. 98 to 2 parts by weight of a polythiol containing at least 2 thiol groups per molecule; the total combined functionality of the carbon to carbon bonds per molecule in the polyene and the thiol groups per molecule in the polythiol being greater than 4; and

3. 0.0005 to 50 parts by weight of a photocuring rate accelerator based upon 100 parts weight of (1) and (2) above. (Preferred range of accelerator is about 0.005 to about 30 parts by weight).

The reactive carbon to carbon bonds of the polyenes are preferably located terminally, near terminally, and- /or pendant from the-main chain. The polythiols, preferably, contain two or more thiol groups per molecule.

Included in the term liquid, as used herein, are those photocurable compositions which in the presence of inert solvent, aqueous dispersion or plasticizer have a viscosity ranging from essentially zero to about million centipoises at 130C.

As used herein polyenes and polyynes refer to simple or complex species of alkenes or alkynes having a multiplicity i.e., at least 2, reactive carbon to carbon unsaturated functional groups per average molecule. For example, a diene is a polyene that has two reactive" carbon to carbon double bonds per average molecule, while a diyne is a polyyne that contains in its structure two reactive carbon to carbon triple bonds per average molecule. Combinations of reactive triple bonds within the same molecule are also operable. An example of this is monovinylacetylene, which is a polyeneyne under our definition. For purposes of brevity all these classes of compounds will be referred to herein as polyenes.

As used herein the term reactive unsaturated carbon to carbon groups means groups which will react under proper conditions as set forth herein with thiol groups to yield the thioether linkage as contrasted to the term unreactive" carbon to carbon unsaturation which means groups when found in aromatic nucleii (cyclic structures exemplified by benzene, pyridine, anthracene, and the like) which do not under the same conditions react with thiols to give thioether linkages. 1n the instant invention products from the reaction of polyenes with polythiols which contain 2 or more thiol groups per average molecule are called polythioether polymers or polythioethers.

Methods of preparing various polyenes useful within the scope of this invention are disclosed in U.S. Pat. No. 3,627,529 assigned to the same assignee. Some of the useful polyenes are prepared in the detailed examples, set forth in the following specification.

One group of polyene compositions are those polyene compositions have a -ene or -yne functionality of at least two which are formed by reacting either:

A. An organic epoxide containing at least two groups in its structure with a member of the group consisting of hydrazine, primary amines, secondary amines, tertiary amine salts, organic acids wherein said group members contain at least one organic substituent containing a reactive ethylenically or ethylynically unsaturated group; or

B. An organic epoxide containing at least one organic substituent containing a reactive ethylenically or ethylynically unsaturated group with a member of the group consisting of hydrazine and an organic material containing at least two active hydrogen functions from the group consisting of:

A second group of polyenes operable in the instant invention is that taught in British Patent No. 1215591 assigned to the same assignee. This group includes those having a molecular weight in the range of 50 to 20,000 a viscosity ranging from 0 to 20 million centipoises at C. of the general formula: [AHX),,, wherein X is a member of the group consisting of and R--C E C; m is at least 2; R is independently selected from the group consisting of hydrogen, halogen, aryl, substituted aryl, cycloalkyl, substituted cycloalkyl, aralkyl, substituted aralkyl and alkyl and substituted alkyl groups containing one to 16 carbon atoms and A 6 isa polyvalent organic moiety free of l) reactive caretc. On the average the polyenesimust contain two or bon tocarbonunsaturationand (2) unsaturated groups more reactive unsaturated carbonito carbon bonds/- in conjugation with the reactive ene or yne groups of molecule and have a viscosity in the range from slightly X.- Thus A may contain cyclic groupings and minor above to about 20 million centipoises at 70C. Inamountsof hetero atomssuch as N, S, P orO but concluded in the term polyenes as used herein are those tains primarily. carbon-carbon, carbon-oxygen or silimaterials which in the presence of an inert solvent, con-oxygen containing chain linkages without any re.- aqueous dispersion or plasticizer fall within the viscosactive carbonto carbon unsaturation. ity range set out above at 70C. Operable polyenes in the instant invention have molecular weights in the in this second group, the polyenes are simple or com- 10 range of about 50 to about 20,000, preferably about plex species of alkenes or alkyenes having a multiplicity 500 to about 10,000.

of pendant, teminally or near terminally positioned re- Examples of operable polyenes from this second active carbon to carbon unsaturated functional group include, but are not limited to: groups per averagemolecule. As used herein for deter- Cr0tylterminated polyurethanes which contain mining the position of the reactive functional carbontov two. reactive double bonds per average molecule in carbon unsaturation, the term terminal means that anear terminal position of the average general formula:

said functional unsaturation is at an end of the. main where x is'at least 1,

chain in the molecule; whereas by near terminal is 2 ethylene/propylene/non-conjugated diene terpolymeant that the functional unsaturationis more than 16 mers, such as Nordel 1040 manufactured. by El ducarbon atoms away from an end of the mainchain in Pont de Nemours and Co., Inc., which contains penthe molecule. The term pendant means that the reacdant reactive double bonds of the formula: tive carbon to carbon unsaturation is located terminally 0 CH CH=CHCH or near terminally ina branch of the main chain as con- 3. the following structure which contains terminal trasted to a position at or near the ends of the. main reactive double bonds:

chain. For purposes of brevity all of these positions will be referred to generally as terminal unsaturation. Z

' CH =CHCH;OC-CHz o-o-crr cr1=c1n The liquid polyenes operable in this second group contain one or more of the following types of nonwhere x is at least 1. aromatic and non-conjugated reactive carbon to car- 4. The following structure which contains near termibon unsaturation: 40 nal reactive double bonds CH (CH)CH=OHGH coc H -ocon CH:CHCH CH (1) (5) where t is at least 1.

. A third group of operable polyenes includes those. E v '=0H I unsaturated polymers in which the double or triple CH=CHZ (7) I bonds occur primarily within the mam chain of the molecules. Examples include conventional elastomers (4 -050H (s) 0=0 (derived primarily from standard diene monomers) l such as polyisoprene, polybutadiene, styrene-butadiene rubber, isobutylene-iosprene rubber, polychloroprene, styrene-butadiene-acrylonitrile rubber and the like; unsaturated polyesters, polyamides, and polyurethanes derived from monomers containing reactive unsaturation, e.g.; adipic acid-butenediol, 1,6-hexanediamine-fumaric acid and 2,4-tolylene diisocyanatebutenediol condensation polymers and the like.

A fourth group of polyenes operable in this invention These functional groups as shown in 1-8 supra are situated in a position either which is pendant, terminal or near terminal with respect to the main chain but are free of terminal conjugation. As used herein the phrase free of terminal conjugation means that the terminal reactive unsaturated groupings may not be linked directly to non-reactive unsaturated species such as 4 1 includes those polyenes in Which the reactive unsatu- E i fi rated carbon to carbon bonds are conjugated with adjacent unsaturated groupings. Examples of operable conand the like so as to form a conjugated system of unsatjugated reactive ene systems include but are not limited urated bonds exemplified by the following structure: to the following:

"1' l t a A few typical examples of polymeric polyenes which contain conjugated reactive double bond groupings such as thosedescribed above are poly(oxyethylene) glycol (600 M.W.) diacrylate, poly(oxytetramethylene) glycol (1000 M.W.) dimethylacrylate, the triacrylate of the reaction product of trimethylolpropane with 20 moles of ethylene oxide, and the like.

As used herein, the term polythiols refers to simple or complex organic compounds having a multiplicity of pendant or terminally positioned SH functional groups per average molecule.

On the average the polythiols must contain two or more Sl-l groups/molecule. They usually have a viscosity range of slightly above to about 20 million centipoises (cps) at 70C, as measured by a Brookfield Viscometer. Included in the term polythiols as used herein are those materials which in the presence of an inert solvent, aqueous dispersion or plasticizer fall within the viscosity range set out above at 70C. Operable polythiols in the instant invention usually have molecular weights in the range about 50 to about 20,000 preferably about 100 to about 10,000.

The polythiols operable in the instant invention can be exemplified by the general formula: R -4Sl-l) where n is at least 2 and R is a polyvalent organic moiety free from reactive carbon to carbon unsaturation. Thus R may contain cyclic groupings and minor amounts of hetero atoms such as N, S, P or 0 but primarily contains carbon-hydrogen, carbon-oxygen, or siliconoxygen containing chain linkages free of any reactive" carbon to carbon unsaturation.

One class of polythiols operable with polyenes in the instant invention to obtain essentially odorless cured polythioether printing plates are esters of thiolcontaining acids of the general formula: l-lS- R COOl-l where R is an organic moiety containing no reactive" carbon to carbon unsaturation with polyhydroxy compounds of the general structure: R -tOHL, where R is an organic moiety containing no reactive carbon to carbon unsaturation and n is 2 or greater. These components will react under suitable conditions to give a polythiol having the general formula:

E T I) odors, are operable in this invention. Examples of the glycolate), ethylene glycol bis ([3 -mercaptopropionate), trimethylolpropane tris (B -mercaptopropionate), pentaerythritol tetrakis (thioglycolate) and pentaerythritol tetrakis (B -mercaptopropionate), all of which are commercially available. A specific example of a preferred polythiol is polypropylene ether glycol bis (B -mercaptopropionate) which is prepared from polypropylene-ether glycol (e.g., Pluracol P2010, Wyandotte Chemical Corp.) and B -mercaptopropionic acid by esterification.

The preferred polythiol compounds are characterized by a low level of mercaptan-like odor initially, and after reaction, give essentially odorless cured polythioether end products which are commercially useful resins or elastomers for printing plates.

As used herein the term odorless means the substantial absence of the well-known offensive and sometimes obnoxious odors that are characteristic of hydrogen sulfide and the derivative family of compounds known as mercaptans.

The term functionality as used herein refers to the average number of ene or thiol groups per molecule in the polyene or polythiol, respectively. For example, a triene is a polyene with an average of three reactive carbon to carbon unsaturated groups per molecule and thus has a functionality (I) of three. A dithiol is a polythiol with an average of two thiol groups per molecule and thus has a functionality (f) of two.

It is further understood and implied in the above definitions that in these systems, the functionality of the polyene and the polythiol component is commonly expressed in whole numbers although in practice the actual functionality may be fractional. For example, a

polyene component having a nominal functionality of 2 (from theoretical considerations alone) may in fact have an effective functionality of somewhat less than 2. In an attempted synthesis of a diene from a glycol in which the reaction proceeds to 100 percent of the theoretical value for complete reaction, the functionality (assuming 100 percent pure starting materials) would be 2.0. lf, however, the reaction were carried to only 95 percent of theory for complete reaction, about 10 percent of the molecules present would have only one ene functional group, and there may be a trace of material that would have no ene functional group, and there may be a trace of material that would have no ene functional groups at all. Approximately percent of the molecules, however, would have the desired diene structure and the product as a whole then would have an actual functionality of 1.9. Such a product is useful in the instant invention and is referred to herein as having a functionality of 2.

The aforesaid polyenes and polythiols can if desired, be formed or generated in situ and still fall within the scope of the instant invention.

To obtain the maximum strength, solvent resistance, creep resistance, heat resistance and freedom from tackiness, the reaction components consisting of the polyenes and polythiols of this invention generally are formulated in such a manner as to give solid, crosslinked, three dimensional network polythioether polymer systems on curing. In order to achieve such infinite network formation the individual polyenes and polythiols must each have a functionality of at least 2 and the sum of the functionalities of the polyene and polythiol components must always be greater than 4. Blends and mixtures of the polyenes and the polythiols containing said functionality are also operable herein.

in general, it is preferred, especially at or near the operable lower limits of functionality in the polyene and polythiol, to use the polythiol and the polyene compounds in such amounts that there is one thiol group present for each double bond, it being understood that the total functionality of the system must be greater than four, and the functionality of the thiol and the diene must each be at least two. For example, if two moles of a triene are used, and a dithiol is used as the curing agent, making the total functionality have a value of five, it is preferable to use three moles of the dithiol. lf much less than this amount of the thiol is used, the curing rate will be lower and the product will be weaker because of the reduced crosslink density. If much more than the stoichiometric amount of the thiol is used, the rate of cure may be higher, if that is desirable, although excessive amounts can lead to a plasticized crosslinked product which may not have the desired properties. However, it is within the scope of this invention to adjust the relative amounts of polyenes and polythiols to any values above the minimum scope disclosed herein which give desirable properties to the cured polythioether.

The photocurable compositions of this invention can be modified so that relatively oleophilic material, such as, stearic acid, are present in the-surface areas of the photocured image areas. Other variations include using allyl stearate as a co-curable additive; using resins which are more oleophilic in character than the bisphenol-A used in several of the specific examples; using allyl alcohol or trimethylol propane diallyl ether in place of diallyl amine to terminate the diepoxide resins, the former being the least water sensitive (hydrophilic); and using oleophilic fillers, e.g., powered polyethylene, which are transparent to U. V. light, thereby not interferring with the photocure.

The photocuring element should be exposed to actinic radiation containing a substantial amount of ultraviolet radiation until substantial photocuring takes place in the exposed areas.

The photocuring reaction can be initiated by U. V.

radiation contained in actinic radiation from sunlight or obtained from special light sources which emit significant amounts of U. V. light. Thus it is possible merely to expose the polyene and polythiol admixture to actinic radiation under ambient conditions or otherwise and obtain a cured solid elastomeric or resinous product useful as image production material. But this approach to the problem results in extremely long exposure times which causes the process in the vask bulk of applications to be commercially unfeasible. Chemical photocuring rate accelerators (photoinitiators or sensitizers or activators) serve to drastically reduce the imaging exposure times and thereby when used in conjunction with various forms of energetic radiation (containing U.V. radiation) yield very rapid, commercially practical cures by the practice of the instant invention. Useful photocuring rate accelerators include benzophenone, acetophenone, acenapthene-quinone, methyl ethyl ketone, thioxanthen-Q-one, xanthen-9-one, 7-H- Benz [de] anthracen-7-one, dibenzosuberone, lnaphthaldehyde, 4,4'-bis-(dimethylamino) benzophenone, fluorene-9-one, l'-acetonaphthone, 2'- acetonaphthone, 2,3-butanedione, anthraquinone, lindanone, 2-tert-butyl anthraquinone, valerophenone,

hexanophenone, S-phenylbutyrophenone, p-morpholinopropiophenone, 4-morpholinobenzophenone, 4-morpholinoseoxybenzoin, p-diacetylbenzene, 4- aminobenzophenone, 4'-methoxyacetophenone, benzaldhyde, a-tetralone, 9-acetylphenanthrene, 2- acetylphenanthrene, lO-thioxanthenone, 3- acetylphenanthrene, 3-acetylindole, l,3,5,-triacetylbenzene, etc. and blends thereof. The photocuring rate accelerators (the third crucial ingredient) are added in an amount ranging from about 0.0005 to about 50 percent by weight of the polyene and polythiol components in the instant invention. Benzophenone is the preferred photocuring rate accelerator. Useful U. V. radiation has a wave length in the range of about 2000 to 4000 angstrom units.

The compositions to be photocured, i.e., converted to asolid continuous tone lithographic printing plate, in accord with the present invention may, if desired, in-

clude such additives as natural or synthetic resins, antioxidants, dyes, inhibitors, activators, fillers, pigments, antistatic agents, flame-retardant agents, thickeners, thixotropic agents, surface-active agents, light scattering agents, viscosity modifiers, extending oils, plasticizers, tackifiers and the like within the scope of this invention. Such additives are usually preblended with the polyene or polythiol prior to or during the compounding step. As is the case with any material which is added to the photocurable polymer composition useful within the scope of the invention, one should take care thatit does not affect the oleophilic or hydrophobic characteristics thereof in a manner which is undesired. Operable fillers include natural and synthetic resins, carbon black, glass fibers, wood flour, clay, alumina, carbonates, e.g., an oxide, e.g., titanium dioxide, hydroxides, silicates, glass flakes, glass beads, borates, phosphates, diatomaceous earth, calcium sulfate, a calcium carbonate, antimony oxide, colloidal carbon, titanium dioxide, various colored pigments, various organophilic silicas, powdered glass, and the like. The aforesaid additives may be present in quantities up to 500 parts or more per parts photocurable polymer composition by weight and preferably 0.0005 to 300 parts on the same basis.

The type and concentration of additives must be selected with great care so that the final composition remains photo-curable under practical conditions of exposure and with commerically feasible time cycles maintained throughout the operation. Additives which block out the passage of U. V. light or which detract from the stability of the photocurable composition must be avoided.

The compounding of the components prior to curing can be carried out in several ways. One useful method of compounding is to prepare by conventional mixing techniques (but in the absence of actinic radiation) a composition consisting of polyene, polythiol, U.V. sensitizer or photoinitiator, and other inert additives. This composition generally can be stored in the dark for extended periods of time. lt could be charged to an aerosol can, drum, tube or cartridge for'subsequent use.

Conventional curing inhibitors or retarders operable in the instant invention include but are not limited to hydroquinone p-tert-butyl catechol; 2.6-ditert-butyl-pmethylphenol phenothiazine and N-phenyl-Z- napthylamine. The majority of the commercially available monomers and polymers used in the photocurable compositions normally contain minor amounts (about 50 to 5000 parts per million by weight) of inhibitors to prevent spontaneous polymerization prior to use in making a printing plate. The presence of these inhibitors in optimum amounts causes no undesirable results in the photocurable layer of this invention.

The molecular weight of the polyenes of the instant invention can be measured by various conventional methods including solution viscosity, osmotic pressure and gel permeation chromatography. Additionally, the molecular weight can be sometimes calculated from the known molecular weight of the reactants. The viscosity of the polyenes and polythiols was measured on a Brookfield Viscometer at 30 or 70C. in accord with the instructions thereof.

The photocurable composition at ambient temperatures can vary from a liquid to a solid state, including a gel or elastomeric state. The photocurable composition may also contain a thickening agent to increase the viscosity of the photocurable liquid polymer. For example, cellulosic derivatives, finely divided silicas, and finely ground fibrous asbestos materials may be used, but it is preferable that a filler be used which will volatilize when the cured photocurable composition is thermally decomposed. The preferred photocurable compositions of the instant invention have viscosities in the range of about 0.25 to about 350 poises and preferably from about to about 150 at or below 130C. The photocurable compositions can also be added as an aqueous emulsion.

The light sensitive materials operable herein can be liquid or solids. They are usually applied to the anodized aluminum surface in solution and then the solvent is evaporated off.

Other suitable radiation sensitive layers which may be employed include silver halide emulsions, bichromated colloids, diazonium compounds and the like.-

In the process of the instant invention a grained or ungrained aluminum or aluminum alloy sheet may be employed. A grained sheet is preferred since this provides better water receptivity. Preferably the sheet should have a surface which has been mechanically or electrochemically roughened so that the non-printing areas of the resulting printing plate retain the fountain solution during printing more easily.

To process a presensitized printing plate made by the process of the instant invention it should be placed under an image bearing transparency and exposed to a source of actinic radiation for example a carbon arc, pulsed xexon lamp or mercury xexon lamp or any other lamp containing a high proportion of UV. light for periods ranging from V. to 6 minutes depending on the distance of the light source from the plate. After exposure, the image is formed by dissolving away or washing away the unexposed portion of the light-sensitive material with a suitable developer. The plate is then treated with a desensitizing solution of gum arabic to prevent the background areas from accepting ink. If desired, the image may be made visible by the use of a lacquer, developing ink or colorant before being used for printing on the press. The plate is now ready for use on a lithographic printing press.

The following examples are intended to illustrate but in no way limit the instant invention. Unless otherwise noted all parts and percentages are by weight. In order to test the plates as rapidly as possible for wear resistance an accelerated wear test was devised. Said test consisted of: overpacking a non-compressible blanket on the press to 7 mils over bearers in combination with an abrasive ink commercially available from Capitol Printing Ink Co., Washington, DC. under the tradename Abrasive Black No. 15745. Said ink consisted of a standard black offset printing ink containing gran ulated lime of greater than 10 microns in diameter in an amount equal to 1.0 oz. lime/pound ink. When printed under the conditions of this test, plates showed the same wear in 20,000 impressions as they would have done in 200,000 impressions with the press run normally packed and with non-abrasive ink.

EXAMPLE 1 An 18 inch X 23 inch X 12 mil sheet of grained aluminum was anodized by immersing the sheet to serve as an anode in a tank containing a 15 percent sulfuric acid electrolyte at a temperature of 24C and wherein an 18 inch X 23 inch X 12 mil sheet of lead served as the cathode. Current was applied to the elctrodes at a density of 20 amps per square feet for 1% minutes. The anodized aluminum sheet was removed from the bath and thoroughly rinsed with water at room temperature and then dried. Analysis of the surface anodized layer indicated the presence of about 221 mg/m of aluminum sulphate. The pore size of the oxide coating was found from electron microscopy to be less than 50 angstroms. The dried anodized aluminum sheet was immediately coated with a composition made up in the following manner. 458 G. (0.23 mole) of a commercially available liquid polymeric diisocyanate sold under the tradename Adiprene L- by E. 1. Dupont de Nemours and Co., were charged to a dry resin kettle maintained under a nitrogen atmosphere and equipped with a condenser, stirrer, thermometer and gas inlet and outlet. 37.8 g. (0.65 mole) of allyl alcohol were charged to the kettle and the reaction was continued for 17 hours with stirring at 100C. Thereafter the nitrogen atmosphere was removed and the kettle was evacuated 8 hours at 100C. 50 cc. dry benzene were added to the kettle and the reaction product was azeotroped with benzene to remove the unreacted alcohol.

This allyl terminated liquid polyene prepolymer had a molecular weight of approximately 2100 and will herein after be referred to as prepolymer A. 2 grams of prepolymer A along with 0.6 grams of dibenzosuberone (photosensitizer) and 0.23 grams of pentaerythritol tetrakis (B -mercaptopropionate) commercially available from Carlisle Chemical Company under the tradename Q-43 were dissolved in 13.3 grams of 2- methoxyethyl ether. The photocurable composition was wiped on the anodized aluminum sheet with a cloth until dry. The plate was then contact exposed through a half-tone negative for one minute to a carbon lamp at a distance of 38 inch and thereafter swab-developed with an aqueous solution consisting of 8 parts Triton X-100 in 100 parts water. The plate was then printed on a Harris Model L B 19 X 25 inch offset press using 60 pound long grain Scott offset paper. The quality of the plate was excellent and it ran fo r 23,000 accelerated wear impressions with no sign of wear. This example shows the ability of a sulfuric acid anodized plate to print efiectively if it is used immediately before the surface becomes unstable.

EXAMPLE 2 A grained aluminum plate was anodized, rinsed and dried according to Example 1, and then cut in half. One

half was stabilized for two minutes in a 15 percent phosphoric acid solution giving 39 mg./m of aluminum phosphate and the other half was untreated. The surface impedance as measured by a Z scope was 1.47 KO for the untreated sample andl.40 K!) for the stabilized sample. After one week .storage, the stabilized plate was stillat 1.40 K0. while the unstabilized plate had increased to 2.45 KB. At the end of the one week period the phosphoric acid treatedplate was coated with the photocurable composition used in Example 1. Following the exposure and development technique of Example 1 the stabilized plate was run on the Harris press for 25,000 accelerated wear impressions without any 1 sign of wear.

The untreated plate was coated and exposed under the same conditions as in Example 1. An attempt to develop the plate as in Example 1 resulted in the plate failing to adhere the cured photopolymer. That is, both the cured exposed and the uncured unexposedareas were removed and no imaged plate was obtained. This example shows the stability of the plate produced by the instant invention'over one anodized in sulfuric acid.

EXAMPLE 3 An aluminum plate was anodized according to Example 1 and cut in half. One half was treated for 2 minutes inan aqueous 15 percent phosphoric acid'bath and-the other half was untreated. Both halves were placed in water at 100C for 15 minutes. After drying, the phosphoric acid treated plate was unchanged (and had a Z of 1.40 K) and could still be used as a plate base whereas the untreated base (with a Z of 10.5 K0) was sealed (as determined by impedance measurements (Z scope) and no longer adhered polymer.

EXAMPLE 4 An aluminum plate was anodized in sulfuric acid according to the procedure of Example 1. The plate was washed in water, dried and then immersed in a aqueous 15 percent phosphoric acid bath for two minutes, followed by a rinse in deionized water. After drying it was coated with the photocurable composition of Example 1 pigmented-with 0.15 grams phthalocyanine blue. The plate was imaged and developed as in Example 1. Following the printingprocedure of Example 1, 25,000 accelerated wear impressions were obtained without any sign of wear on the plate.

For a comparison an aluminum plate, anodized in phosphoric acid without any subsequent treatment, resulting in an aluminum oxide coating having a pore size of in the range 150 500 angstroms. The anodized aluminum surface layer containedabout 97 mg./m of aluminum phosphate and was exposed and developed as above using the same photocurable composition. When run under the same conditions on the Harris press, the plate showed signs of wear after 15,000 accelerated wear impressions.

EXAMPLE 5 An 18 inch X 23 inch X 12 mil sheet of grained aluminum was anodized byrimmersing the sheet to serve as an anode in a tank containing a 15 percent sulfuric acid electrolyte at a temperature of 24C and wherein an 18 inch x 23 inch X 12 mil sheet of lead served as the cathode. Current was applied to the electrodes at a density of amps per square feet for l A minutes. The anodized aluminum sheet was removed from the bath and thoroughly rinsed with water at room temperature and then dried. The anodized sheet was then stabilized by immersion in a bath of 25 percent phosphoric acid maintained at room temperature for a period of 3 minutes. The thus stabilized sheet was removed from the bath and rinsed in deionized water and then dried.

Analysis of the surface anodized layer indicated the presence of about 395 mg./m of aluminum sulphate and about 48.5 mg./m of aluminum phosphate. The pore size of the oxide coating was found from electron microscopy to be less than 50 angstroms. The dried anodized aluminum sheet was coated with a composition made up in the following manner. 897.8 gms (3.8 moles) of commercially available trimethylolpropane diallylether, sold by Proctor Chemical Company, and 6.2 gms stannous octoate (catalyst) was charged to a dry resin kettle maintained under a nitrogen atmosphere andequipped with a condenser, stirrer, thermometer, dropping funnel and gas inlet and outlet. 348 gms. (2 moles) of commercially available toluene diisocyanate was charged to the dropping funnel and dripped into the resin kettle at a rate to maintain the temperature between C80C. After addition, the reaction was allowed to stir at 70C80C. for an additional 2 hours undernitrogen. This allyl terminated liquid polyene prepolymer had a molecular weight of 602 and will be referred to herein after as Prepolymer B. 2 grams of prepolymer B along with 1.1 grams dibenzosuberone (photosensitizer) and 1.63 grams of pentaerythritol tetrakis (B -mercaptopropionate) commercially available from Carlisle Chemical Company under the tradename 0-43 were dissolved in 27.8 grams of 2- methoxyethyl ether. The photocurable composition was wiped on the anodized aluminum sheet with a cloth until dry. The plate was then contact exposed through a half tone negative for one minute to a carbon lamp at a distance of 38 inch and thereafter swab-developed with an aqueous solution consisting of 8 parts Triton X-lOO in parts water. The plate was then printed on a Harris Model L B 19 X 25 inch offset press using 60 pound long grain Scott offset paper. The quality of the plate was excellent and it ran for 25,000 accelerated wear impressions with no sign of wear.

EXAMPLE 6 An aluminum plate was anodized and rinsed according to Example 1, and then cut in half. One half was stabilized for 3 minutes in an 18 percent phosphoric acid solution, rinsed and dried and the other unstabilized half only dried. Both plates were stored for one week after which time both were hand coated with full strength Kodak Photo Resist (KPR) and wiped dry. The plates were contact exposed to a carbon lamp at a distance of 38 inch through a halftone negative for 1 minute and developed with 1:2 KPR Developer/KPR Thinner followed by 1:1 KPR Developer/Denatured .Alcohol, then desensitized with 1:1 LTF Post Nital Solution/Desensitizing Etch. Attempts to rub up the plate with P.D.I. Spray Rub UP ink gave a completely scummed background to the untreated sample while the phosphoric acid treated sample rubbed up normally and went on to print 23,000 accelerated wear impressions with no sign of sharpening or scumming.

EXAMPLE 7 Two aluminum plates, one anodized and stabilized and the other only anodized as in Example 6 were coated with Harold M. Pitman Co. ST Diazo material and dried. After contact exposure to a carbon arc under a half-toned negative for 100 seconds, the plates were developed with Pitman Co. ST Super D developer. Again, the untreated plate scummed badly in the background areas while the H PO treated plate produced a clean background area with a well defined image area. This plate was subjected to 20,000 accelerated wear impressions with little loss of image fidelity and no background scumming.

EXAMPLE 8 Two uncoated aluminum plates, one anodized and stabilized and the other only anodized according to Example 6 were coated with polyvinyl alcohol stabilized polyvinyl acetate latex sensitized with 0.1 percent ammonium dichromate and dried. After contact exposure to a carbon lamp for 2 minutes through a halftone negative, the plates were developed with tap water and desensitized with normal pressmans desensitizing etch. Both were then rubbed up with P.D.l. spray rub-up ink at which point the untreated plate again showed scum in the background area, indicating imcomplete removal or possible precuring of unexposed photosensitive material. The H PO stabilized plate was subjected to 35,000 accelerated wear impressions without any sign of wear or failure.

EXAMPLE 9 Two aluminum plates, one anodized and stabilized, the other only anodized by the procedure of Example 6 were coated in a darkroom with a silver halide aqueous emulsion containing 25 percent Ag N 0.8% photographic grade gelatin and 0.02% K Cr O by soaking for 1 minute, squeegeeing off the excess, and drying. Then both plates were soaked for 1 minute in an aqueous solution of each KBr and K Cr O rinsed well under running water and dried at 40C for k hour. After exposure to visible light for 20 seconds under a half-tone negative, both plates were developed using a normal silver halide type film developer. The untreated plate showed a general background fog while the H PO treated plate did not. The treated plate printed 10,000 accelerated wear impressions without loss of image fidelty.

The following example will show the use of the instant invention in producing a letter press printing plate.

EXAMPLE 10 A grained aluminum plate anodized and stabilized as in Example 2 was used as a substrate for a mil thick layer of the photocurable composition of Example 5 except that no Z-methoxyethyl ether was added as a solvent. The layer was exposed through a line and halftone negative with an air gap of 12 mils between the surface of the photocurable composition and the negative to actinic light from a 4,000 watt Ascorlux pulsed xenon are printing lamp, commercially available from American Speed Light Corporation placed inches above the negative. The exposure was for 1 minutes during which time the liquid photocurable composition solidified in the image areas. The plate was developed in an aqueous solution consisting of 8 parts Triton X- 100 in 100 parts water in a bath ultrasonically activated to the degree necessary to cause cavitation, i.e.

in the energy level range of 18-40 kilocycles/sec. at a' temperature of C to remove the uncured material. The cured imaged areas obtained had outstanding adhesion to the aluminum plate. The plate was inked and employed in letter press printing on a Davidson Press Model 816 manufactured by Davidson Corporation, Chicago, Illinois. The printing resulted in distinct and separate lines and the dots in the half-tone areas had excellent definition.

To show the wear resistance of the stabilized anodized aluminum plate of the instant invention as compared to other aluminum plates anodized by other procedures the following comparisons were made.

EXAMPLE 11 8 inch X 8 inch X 12 mil sheets of grained aluniinum were subjected to the following treatment:

Sheet A was immersed as a anode in a tank containing a 15 percent sulfuric acid electrolyte at a temperature of 40C employing a lead cathode of the same dimensions. Current was applied to the electrodes at a density of 50 amps per square foot for 1.5 minutes. The sheet was removed from the bath, thoroughly rinsed with water and dried. Analysis of the surface indicated the presence of 1109 mg./m aluminum sulphate. The sheet was cut in a 6 inch diameter circle and weighed.

Sheet B was immersed to serve as an anode in a tank containing 42 percent phosphoric acid electrolyte at a temperature of 25C using a lead cathode of the same dimensions. A current density of 24 amps per square foot was applied for 6 minutes. The sheet was removed, rinsed thoroughly in water and dried. Analysis of the surface indicated the presence of 97 mg./m aluminum phosphate. The sheet was cut in a 6 inch diameter circle and weighed.

Sheet C was anodized by immersing the sheet to serve as an anode in a tank containing a 15 percent sulfuric acid electrolyte at a temperature of 21C using a lead cathode of the same dimensions. Current was applied to the electrodes at a density of 27 amps per square foot for 2 minutes. The sheet was removed from the bath, thoroughly rinsed with water and then stabilized by immersion in a bath of 25 percent phosphoric acid at room temperature for a period of 3 minutes. The sheet was removed from the bath, rinsed thoroughly in water and dried. Analysis of the surface indicated the presence of 520 mg./m aluminum sulphate and 50 mg./m aluminum phosphate. The sheet was cut in a 6 inch diameter circle and weighed.

The sheets were individually subjected to a wear resistant test in accord with ASTM D 1044-56 using a Taber caliber CS-l7 abrading wheel with a 250 gram counter balanced weight on the arms. A refacing disc (180J A1 0 on cloth was used to reface the wheels for 10 cycles after every 50 cycles. The samples were run 150 cycles and were weighed after every 50 cycles. The results showed that after 150 cycles, sheet A lost 1.8 mg; sheet B lost 1.4 mg. and sheet C lost 0.3 mg.

What is claimed-is:

l. A printing plate comprising a support with an anodized aluminum hydrophylic printing surface and an ink receptive coating layer directly thereon, said anodized aluminum surface comprising a cellular pattern of aluminum oxide having cells with pourous openings of about 5 to 100 angstroms in average diameter and said surface comprising about 20 to 5000 mg./meter aluminum sulphate and about 1 to 50 mg./meter aluminum phosphate, said ink receptive coating layer comprising an image forming material selected from 2. The printing plate of claim 1 wherein the light sensitive material is a diazo compound.

3. The printing plate of claim 1 wherein the light senthe group consisting of light sensitive materials and sil- Sitive material is a photopolymef- 

2. The printing plate of claim 1 wherein the light sensitive material is a diazo compound.
 3. The printing plate of claim 1 wherein the light sensitive material is a photopolymer. 